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The generated server-side decoder and encoder for a void procedure
argument or result are named after the RPC program (for example,
nfs_svc_decode_void). xdrgen derives that prefix from the program
name alone, not the version, so two versions of one program built
into the same module emit the identical symbol. NFSv2 and NFSv3
both declare program NFS_PROGRAM; once both are converted, fs/nfsd
fails to link with multiple definitions of nfs_svc_decode_void and
nfs_svc_encode_void.
A void handler carries no program- or version-specific behavior:
each merely forwards to xdrgen_decode_void() or xdrgen_encode_void().
Define one shared pair, xdrgen_svc_decode_void() and
xdrgen_svc_encode_void(), in the xdrgen builtins, and stop the
program generator from emitting a per-program void handler.
lockd is the one in-tree consumer that already emits per-program
void handlers, so regenerate the NLMv3 and NLMv4 XDR code to drop
nlm_svc_{decode,encode}_void() and nlm4_svc_{decode,encode}_void()
and point both procedure tables at the shared handlers. The shared
handlers are identical to the generated ones they replace, so no
wire behavior changes.
Only the server (svc) handlers are affected. The client-side void
stubs remain static and per-program, so they do not collide.
Link: https://patch.msgid.link/20260712193122.116845-3-cel@kernel.org
Signed-off-by: Chuck Lever <cel@kernel.org>
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struct svc_service has a .vs_xdrsize field that is filled in by
servers for each of their RPC programs. This field is supposed to
contain the size of the largest procedure argument in the RPC
program. This value is also sometimes used to size network
transport buffers.
Currently, server implementations must manually calculate and
hard-code this value, which is error-prone and requires updates
when procedure arguments change.
Update xdrgen to determine which procedure argument structure is
largest, and emit a macro with a well-known name that contains
the size of that structure. Server code then uses this macro when
initializing the .vs_xdrsize field.
For NLM version 4, xdrgen now emits:
#define NLM4_MAX_ARGS_SZ (NLM4_nlm4_lockargs_sz)
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
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"xdrgen definitions" was not providing a definition of a symbolic
constant for the RPC program number being defined.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
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I noticed that "xdrgen source" reorders the procedure encoder and
decoder functions every time it is run. I would prefer that the
generated code be more deterministic: it enables a reader to better
see exactly what has changed between runs of the tool.
The problem is that Python sets are not ordered. I use a Python set
to ensure that, when multiple procedures use a particular argument or
result type, the encoder/decoder for that type is emitted only once.
Sets aren't ordered, but I can use Python dictionaries for this
purpose to ensure the procedure functions are always emitted in the
same order if the .x file does not change.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
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Add a Python-based tool for translating XDR specifications into XDR
encoder and decoder functions written in the Linux kernel's C coding
style. The generator attempts to match the usual C coding style of
the Linux kernel's SunRPC consumers.
This approach is similar to the netlink code generator in
tools/net/ynl .
The maintainability benefits of machine-generated XDR code include:
- Stronger type checking
- Reduces the number of bugs introduced by human error
- Makes the XDR code easier to audit and analyze
- Enables rapid prototyping of new RPC-based protocols
- Hardens the layering between protocol logic and marshaling
- Makes it easier to add observability on demand
- Unit tests might be built for both the tool and (automatically)
for the generated code
In addition, converting the XDR layer to use memory-safe languages
such as Rust will be easier if much of the code can be converted
automatically.
Tested-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
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Chuck Lever
Chuck Lever